Patent application WO2007/113815 titled “System and Method for Optical Positioning and Guidance of a Rigid or Semi-Flexible Tool to a Target” by Pinhas Gilboa, describes an optical guidance system based on a patch attached to the skin of a patient. The patch provides an arrangement of fiducial points. These fiducial points enable a visible area of interest to be located by a person, and associated with relevant imaging data. The optical guidance system coordinates the imaging data with the visible area of interest and provides guidance for a person inserting a medical tool to reach a target that is not directly visible. These fiducial points on the patch include colored markings for optical image processing associated with high-contrast markings for an appropriate imaging system.
In the context of this document, the term colored markings refers to markings that reflect electromagnetic energy in the visible and near-visible spectrums, including the infrared and ultra-violet spectrums. Colors visible to the human eye include the commonly known yellow, blue, red, green, and others. Visible, infrared and ultra-violet colors are detectable by CMOS and CCD technologies. These colors are detectable by an optical imaging system.
High-contrast markings are markings that create sufficient contrast to be readily visible under non-visible imaging techniques such as X-ray and magnetic resonance imaging (MRI). Suitable high-contrast substances that may be used to produce such markings are known in the industry and used in various forms. When a high-contrast radio-opaque substance is placed between a source of appropriate radiation and a surface sensitive to that radiation, the high-contrast substance prevents exposure of specified portions of the sensitive surface. This technique results in the shape of the substance appearing on the resulting image. This image is known as a radiograph. Other radiations can be used for the same process, including gamma rays, Roentgen rays, radium rays, and other nuclear radiation. Radio-opaque imaging systems include X-ray and computerized tomography (CT scan). Similarly, when a high-contrast magnetic substance is used in an MRI scan the shape of the substance appears in the resulting MRI image. Substances such as Gadolinium containing agents and Ultrasmall Supermagnetic Iron Oxide Particles are currently used in the industry. Other imaging techniques include positron emission tomography (PET scan) and fluoroscopy.
It is known that, in color image processing, the color, also known as the tint, should be accurate. The patent application by Gilboa teaches that it is preferable that each of the optical fiducial points is a specific color for easier differentiation by color segmentation. The patent application suggests techniques to produce combinations of color marking and high-contrast markings.
One suggestion is to embed a high-contrast substance in a flat plastic disk and then print color markings on the disk. Preferably, the positions of the markings for the high-contrast imaging system coincide with the optical fiducial points so that the optical fiducial points are directly derived from the scanned data. This device requires the use of two different production techniques. The use of two different production techniques is less preferred than using one production technique because of the additional expense and complexity of production. The resulting plastic disk is also limited in flexibility due to the requirement to embed a substance in the disk. The use of a device that is limited in flexibility is less preferred than using a flexible device because the flexible device can be used in more areas.
A device for marking cutaneous landmarks is disclosed by DeSena in U.S. Pat. No. 5,193,106, X-Ray Identification Marker. This patent teaches the importance of highlighting a visible area of interest with a marker that is easily seen on a radiograph of the internal, or non-visible, related area. The patent also presents techniques to mark an area of interest, converting a visual localization to a radio-opaque localization. One example is a doctor marking a visible area of interest on a patient's body with a visual marking that is also radio-opaque. When the patient is subsequently X-rayed, the visible area of interest that the doctor identified is indicated on the resulting radiograph. This device comprises a black radio-opaque material on an adhesive tape. The purpose of the device is to refer to a visible area of interest on the foot of a patient and enable association of this area with subsequent radiographic imaging data. This device consists of only radio-opaque markings. The device does not suggest a method for color markings and does not provide the precision necessary to guide a rigid or semi-flexible tool to a target.
A possible method for producing high-contrast markings is to use techniques that have been developed for printing electronic printed circuit boards (PCBs). In these techniques, the printing is performed chemically by masking and etching a layer of copper. This technique can be used for producing the high-contrast markings, but is only suitable for printing on substrates that are rigid or semi rigid. Semi rigid substrates have a stiff internal structure that maintains their form. This technique cannot be used for printing on a flexible patch. A flexible patch can be bent without injury or damage.
For printing on flexible materials, a technique such as offset printing or silkscreen printing is preferred. Other techniques such as inkjet printing are also possible. Printing can be done with a dye that is both colored and high-contrast. A dye for printing color high-contrast markings, in the form of a paste or liquid can be prepared by mixing pigment with high-contrast ingredients. For example, to produce high-contrast black dye base suitable for printing, a mix of Lead (Pb) powder in clear liquor can be used. To produce high-contrast white dye base suitable for printing, a mix of Barium Sulfate (BaSO4) in clear liquor can be used. Other heavy metals may also be used to provide high-contrast properties. Adding pigment to these high-contrast pastes results in a colored high-contrast dye.
These dyes may be easily printed using known techniques on rigid or flexible materials. However, the high-contrast ingredients inevitably change the original tint of the pigment. The tint may be lightened because the tint of the ingredients dilutes the color density of the dye, or darkened because the tint of the ingredients thickens the color density of the dye. The change depends on the color and density of the ingredients used. Accurate color is difficult to achieve with this process.
There is therefore a need for a method to print accurate color markings associated with high-contrast markings. The current embodiment provides such a method.